Process for the separation of trimethylamine from mixtures of monomethylamine and dimethylamine



May 31', 1938.

LE ROY U. SPENCE PROCESS FOR THE-SEPARATION OF TRIMETHYLAMINE FROM MIXTURES OF MONOMETHYLAMINE AND DIMETHYLAMINE 1 Filed Jan; 6, 1937 3 Sheets-Sheet Il- 5OLUB|LlTYar NETHYLAMINES m WATER. AT 0 Luawaa lSO IIO

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TEHPERATU R E C TEMPERATURE C LE ROY u. SPENCE 7 PROCESS FOR THE SEPARATION OF TRIMETHYLAMINE FROM MIXTURES OF MONOMETHYLAMINE AND DIMETHYLAMINE Filed Jan. 6, 1937 3 Sheets-Sheet 2 5OLU8| LITYMH ETHYLAHINE lN WATER AT 100 LBS-GAUGE IO 40 so so I60 MOL z AMINE sowsmmF METHYLAMINES m WATER AT 150 maazwae IOU TRIMETHYLAM'NE 'm Y 5O L hINE J III"Illlllilllllllf 0 lo 20 3O 40 L SOME (a 60 so |oo.

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PROCESS FOR THE SEPARATIONOF TRIMETHYLAMINE FRO Y LAMINE AND DIMETHYLAM INE IIXTURES OF MONOMETHY 3 Sheets-$heet 3 Filed Jan. 6, 1937 204-060 aamomnoxaolwzpo mar ues 6E PRE55URE 1 frweizior Patented May 31, 1938 v 2,119,474

UNITED STATES PATENT OFFICE PROCESS FOR THE SEPARATION OF TRI- METHYLAMJNE FROM MIXTURES OF MONOMIETHYLAMINE' AND DIMETHYLA- IVIINE Le Roy U. Spence, Cheltenham, Pa.., 'assignor to Rohm & Haas Company, Philadelphia, ya.

Application January 6, 1937, Serial No. 119,199 6 Claims. (Cl. 260-127) This invention relates to a process for sepa- Figure 4 shows it at 150 pounds gauge.- rating trimethylamine from its mixtures. with In Figure 5 the upper, lower and preferred both monomethylamine and dimethylamine, par-' temperatures useful in the'process herein disticularly from those mixtures obtained by the closed are graphically illustrated.

5 catalytic synthesis of the methylamines from An inspection of Figure 1 shows that at zero '5 methanol and ammonia. pounds gauge as the temperature is increased,

When a mixture of methanol and ammonia is the solubility of trimethylamine in water dimin passed over a dehydrating catalyst at reacting ishes much more rapidly than does the solubility temperatures, the reaction product is a'mixture of either monomethylamine or dimethylamine.

of the three amines plus water, unreacted meth- At temperatures below about 18 C. trimethyl- 10 anol and ammonia, andsome formaldehyde. The amine is more soluble than monomethylamine. less volatile components of the mixture, water, At 18 C. their solubilitycurves cross and on furmethanol, and formaldehyde, can be easily sepather increase in temperature the solubility of trirated from the methylamines by distillation or methylamine becomes much less than that of '15 partial condensation. The more volatile ammonomethylamine. At about 20 C. the solubilmonia can also be separated by distillation, but ity of trimethylamine is roughly eight-ninths that as ammonia forms a constant boiling mixture of monomethylamine and one-half that of diwith trimethylamine, some of the latter is also methylamine. At 40 C. the solubility of triremoved with the ammonia. This, however,'is methylamine falls to abgut one-fifth that of not objectionable as the usual practice is to remonomethylamine and one-sixth that of dimeth- 20 turn the ammonia with added methanol to the ylamine. At still higher temperatures, for inreaction chamber and any trimethylamine that stance, at 70 C. the solubility of trimethylamine is is mixed with it will pass through unchanged and only one-eighth that of monomethylamine and again appear in the product. less than one-fifth that of dimethylamine. In To separate the three methylamines from one connection with this graph, it is interesting to 25 another is however, a more difficult problem, due observe how the monomethylamine curve crosses partially to their boiling points being very close, both the dimethylamine curve and the trimethylbut'more particularly to the fact that trimethylamine curve. amine forms constant boiling mixtures with both Reference to Figures 2, 3 and 4 shows that monomethylamine and dimethylamine. The forchanges in pressure do not materially change the 3 niation of these constant boiling mixtures makes general contour of the three curves, but only ordinary distillation methods inapplicable to a move them along the temperature axis. complete separation of the mixture. Compli- It will also be observed from Figure 1 that at cated methods involving a series of distillations zero pounds gauge there is a wide difference in at difierent pressures have been proposed. So relative solubility of the three amines at tem- 35 also has a process in which sufficient ammonia peratures ranging from 25 C. to about 90 C. is added to the mixture to remove all the tri- At temperatures below 25 C. the solubility of trimethylamine as a constant boiling mixture. methylamine approaches that of .monomethyl- This latter process while efficient, has the disamine very rapidly and' at temperatures above 40 advantage that it makes necessary the separa- 90 C., the solubilities of all the amines rapidly- 4o tion of the trimethylamine from the ammonia. fall to zero. In Figure 2 a comparative temperav In an efiort to develop a practical and more ture range extends from about C. to 123 C. eflicient method of separating the mixturaImade In Figure 3 the range is from 90 C. to'about a study of the relative solubilities of the three 157 C., and in Figure 4 from 105 .C. to 175 C.- 45 metlrvlamines in water and discovered the sur- .In each instance there is a. temperature range 45 prising fact that changes-in temperature mateextending over to '70 centigrade degrees, rially alter the relative solubility of the three. throughout which there is a wide difference in The results of this study are graphically shown .the solubilities of trimethylamine and mono in Figures 1 to 4 of the drawings. methylamine or dimethylamine. That tempera- 50 In the drawings, Figure 1 is a graph showing ture range in each instance extends from 10 to 50 the effect of temperature on'the solubility of the -80 degrees centigrade beneath the boiling 1 three methylamines at zero gauge pressure. I point of water at the given pressure.

Figure 2 shows the same relationship at a pres- In the present inventionthis great difference sure of 30 pounds gauge. in solubility within the stated temperature range' 55 Figure 3 shows it at pounds gauge, and I is utilized to separate the trimethylamine from 55 monometlrvlamine and dimethylamine. In general it consists in bringing a mixture of the three A methylamines in contact with a quantity of water insufiicient to dissolve them completely, and controlling the temperature so that it is within the range where the difference in their solubilities makes possible a separation of the trimethylamine. When a mixture of gases is brought in contact with a quantity of liquid insufficient to dissolve them completely, they go into solution in proportion to their concentration in the mixture and to their solubilities. The gases in solution will therefore contain a greater proportion of the more soluble component than did the original mixture, and the undissolved gases will be proportionately more concentrated in the less soluble component.- In thefollowing example this principle is illustrated when applied to a'mixture of methylamines at a temperature where trimethylamine is much less soluble than dimethylamine or monomethylamine.

Example 1.A mixture of amines containing 59.5% monomethylamine, 28% dimethylamine, 12.3% trimethylamine, and 0.2% ammonia, was withdrawn from a cylinder and passed into water held at 79 C. and atmospheric pressure. The

composition of the amines in solution was determined and foundto be 72.6% monomethylamine, 23.4% dimethylamine, and 3.9% trimethylamine. The process therefore reduced the t-rimethyle amine content of the original mixture from 12.3% to 3.9%. v

By stripping the solution of the dissolved "amines and repeating the absorption on both undissolved and-stripped gases, a substantially complete separation of the trimethylamine from monomethylamine and dimethylamine can be effected. In practice, the repeated absorption and stripping is preferably carried out in a packed column or bubble cap column or similar device into which water is fed at the top and amines at an intermediate level. Heat applied at the bottom of the column strips the water of the small amount of trimcthylamine that reaches it. As the gaseous amines rise in the column they are absorbedin' proportion to their concentra- :ion andrelative solubility. The mixture thereby becomes gradually richer in trimethylamine as it ascends the column and is substantially pure .whenit leaves the top. The liquid with its absorbed amines, as it descends the column, contacts gas in which the concentration of tri.. methylamine isi below the equilibrium point,

whereupon it gives up the. dissolved trimethy'lamine.

In the operation of such a column to separate methylamines by the present invention, the temperatures at the top and bottom should be preferably from 10 to 60 Centigrade degrees apart, but both within the range of from 10 to -80 degreesbentigrade below the boiling 'point of water at the pressure used. The rateat which the mixture is fed to the column will'depend upon itssize and capacity and be below the rate at which flooding or entrainment will occur.

rate 'at which'undissolved amines are taken oil at the top of the column is adjusted inaccordance with the input rate and should preferably approximate that fraction of the input equal to the fraction of trimethylamine in the feed. The

.undissolved amines are preferably passed through a partial condenser, the function of which is to condense and return, to the column the water vapor carriedofi' with the amines. The temcontrolled perature at the top of the column is .With 12.6%

2,119,474 H by the temperature of the 'water fed in at this proper quantity of amines.

In the following examples, given to illustrate the process, a column twoinches in diameter, twenty feet long, packed with x A stoneware rings, was used. The column was made in two sections, the lower one being seven feet and the upper one thirteen feet long. The mixture of amines was introduced at the top of the seven-foot section. Water was fed into the top of the column at a regulated temperature. The

water saturated with amines was collected in a pot at the bottom of the column. The undissolved amines werefremoved from the top of the column through a partial condenser and passed to a receiver.

Example 2. The amine mixture used contained 55.5% monomethylamine, 26.2% dimethylamine, 14.0% trimethylamine and 4.3% water and methanol. This was fed into the column at a rate of 24.9 lbs. per hour. The temperature in the pot was held at C. and the rate of water feed at the top of the column was adjusted to hold the pressure in the unit-at 50 pounds gauge. The temperature of thewater fed into the top of the column was held at 83 C:- Amines were taken off at a rate of 2.0 pounds per hour through the partial condenser. The cooling on the partial condenser was adjusted to keep the top of column temperature at 85 C. The amines taken oil were 94.6% pure trimethylamine. The amines collected in' the pot (in solution in water) contained only 7.3% trimethylamine as compared with the original 14.6% trimethylamine (on the anhydrous basis).

Example 3.A mixture of amines containing 4 51.6% monomethylamine, 32.3% dimethylamine,

and 12.1% trimethylamine, and 4.0% water and methanol. was used. This was fed into the column at a rate of 22.8 pounds per hour. The tem perature in the pot was held at 134 C. and the adjusted tohold the top of column temperature at 102? C. The amines taken oil were 97.5% pure trimethylamine, and the trimethylamine removed was 75% of. the total trimethylami'ne put in. The amines collected in the pot contained only 3.5% trimethylamine as compared in the feed (anhydrous basis). Ezrample 4.The mixture of amines used contained 57.2% monomethylamine, 28.7% dimethylamine, 12.6% trimethylamine and 1.5% water. and methanol. This was fed into the column at a rate of 24.3 pounds per hour. The-temperature of the pot was held at- 144 C. and the water feed was regulated to hold the pressure t at pounds. The temperature of the water feed was 108 C. v Amines were taken oil at a rate of 2.97 pounds per hour. The-cooling on the partial condenser was. regulated to hold the top of column. temperature at 112 C. The amines taken 01f were 97.2% pure trimethylmine, and the trimethyiamine removed was i% of the total trimethylamine put in. The mines collected in the pot contained only 0.9% rimethylamine as compared with 12.8% in the eed (anhydrous).

It is evident that by selecting the proper op- :rating temperatures the process may be carried rut at any desired pressure. Preferably the pres- ;ure should be high enough so that the trimethylimine coming from the top of the column can be :ondensed with ordinary cooling water. At pres- ;ures above 40 pounds gauge this canreadily be done. If for any reason it is desirable to operate below 40 pounds, the trimethylamine can be absorbed in water and recovered as a solution or condensed by refrigeration. In using the process in conjunction with a plant for producing three methylamines, the higher pressure would be most useful. In such a plant the still used for recovering and returning unreacted ammonia to the reaction chamber is ordinarily operated at a pressure of from 200- to 250 pounds gauge, sothat ordinary cooling water can be used to condense the ammonia. The mixture of methylamines obtained as bottoms from that still could then be transferred through a pipe line to a unit for separating the trimethyiamine in accordance with the present invention, operating at- 150 to 1'75 pounds pressure. At that pressure the trimethyiamine coming from the top of the column could readily be condensed by ordinary cooling water and the solution of dimethylamine and trimethylamine obtained as bottoms could be allowed to flow to a stripping column operating at 125 to 150 pounds pressure. The anhydrous amines from the stripping column could then be led into a fractionating column operating at 100 pounds pressure where the monomethylamine and dimethylamine could be separated. Thus, by operating the various units in the system at gradually reduced pressures, pumping the amines from one unit to another is avoided. Also, by

' two choices of temperature using pressures of the order of those indicated, ordinary cooling water can be used to condense the various fractions, thereby avoiding the need of refrigeration.

I have herein given a detailed description of my process as it is applied to the separation of trimethyiamine from its mixtures with both monomethylamine and dimethylamine. It is, however, also applicable, if the proper temperature is selected, to two-component mixtures of trimethyiamine and dimethylamine, of trimethyiamine and monomethylamine, and even of dimethylamine and monomethylamine. For the separation of a mixture of trimethylamine and either dimethylamine or monomethylamine, the operative temperature range is substantially that of the three-component mixture, i. e., from to 75-80 degrees centigrade beneath the boiling point of water at the pressure employed, although with dimethylamine the minimum temperature may be slightly below this range. For the separation of dimethylamine and monomethylamine, ranges are available. I have shown in the solubilitycurves that the sure of over 40 pounds gauge and at a curves for mono and di cross each other. This point is approximately 50 C. below the boiling point of water. By operating in the range between this point and the boiling point of water, I can separate dimethylamine as the least soluble gas. By operating in the range between this point and the boiling point of dimethylamine, I can separate monomethylamine as the least soluble gas.

I claim:

1. The process of'separating trimethyiamine from a mixture of the three methylamines which comprises passing the mixture into a column at an intermediate point thereof, passing water down the column in quantities suiificient to dissolve substantially all the monomethylamine and dimethylamine but insufficient to dissolve the whole mixture, and adjusting the temperature throughout said column so that it is within the range'from 10 to '75 degrees centigrade below the boiling point of water at the pressure used.

2. The process of separating trimethylamine from a mixture of the three methylamines which comprises passing the mixture into a column operating under a pressure above 40 pounds gauge at an intermediate point thereof, passing water down the column in quantities suilicient to dissolve substantially all the monomethylamine and. dimethylamine but insufiicient to dissolve the whole mixture, and adjusting the temperature throughout said column so that it is within the range from 10 to '75 degrees centigrade below the boiling point of water at the pressure used.

3. The process of separating trimethylamine from a. mixture of the three methylamines which comprises selectively absorbing the monomethylamine and dimethylamine in water by passing the mixture in contact with a stream of water flowing counter-current thereto at a temperature of from 10 to 75 degrees centigrade below the boiling point of water at the pressure employed.

.4. The process of separating trimethylamine from a mixture of the three methylamines which comprises selectively absorbing the monomethylamine and dimethylamine in water by passing the mixture in contact with a stream of water flowing counter-current thereto under a pressure of over 40 pounds gauge and at a temperature of from 10 to '75 degrees centigrade below the boiling point of water at the pressure employed.

5..The process of separating trimethyiamine from a mixture of the three. methylamines which comprises selectively absorbing the monomethylamine and dimethylamine in water at a temperature of from 10 to '75 below the boiling point of water ,at the pressure employed.

,6. The process of separating trimethylamine from a mixture of the three methylamines which comprises selectively absorbing the monomethylamine and dimethylamine in water under a prestemperature of from 10 to 75 degrees centigrade below the boiling point of water at the pressure LE ROY U. SPENCE.

degrees centigrade employed. 

